This section introduces aspects that may be helpful in facilitating a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admission about what is in the prior art.
When a data volume such as a data packet is transmitted initially by radio frequency signals from a first transceiver apparatus via a transmission channel such as a wireless transmission channel to a second transceiver apparatus, several effects such as scattering, fading and/or power decay usually have an impact on the transmitted signal at a location of the second transceiver apparatus and therefore, modified radio frequency signals or in a worst case no radio frequency signals are received by the second transceiver apparatus so that the second transceiver apparatus may not be able to recover error-free the data packet by a single transmission. For solving this problem, several retransmission techniques with one or several further retransmissions from the first transceiver apparatus to the second transceiver apparatus have been developed.
HARQ (HARQ=hybrid automatic repeat request) with chase combining or incremental redundancy is widely used in modern packet based wireless communication systems such as UMTS systems (UMTS=Universal Mobile Telecommunication Systems), HSPA systems (HSPA=High Speed Packet Access) or LTE systems (LTE=Long Term Evolution). HARQ is used in these systems in conjunction with adaptive modulation and coding so as to compensate for transmission errors caused by imperfect link adaptation. Imperfect link adaptation causes significant throughput degradation as compared to the theoretical limits, despite of using HARQ. With HARQ, typically a CRC check (CRC=Cyclic Redundancy Check) is performed at the second transceiver apparatus upon reception of a first transmission of an encoded data packet and the result of the CRC check, PASS or FAIL, is reported to the first transceiver apparatus as an ACK (ACK=acknowledgement) or a NACK (NACK=Negative Acknowledgement), respectively. In case of NACK, the first transceiver apparatus performs a retransmission of the data packet to the second transceiver apparatus and soft combining of the codewords of the received first transmission and the received retransmission is performed by the second transceiver apparatus before the decoding. Soft combining improves error rate performance as compared to simply discarding the first transmission attempt at the second transceiver apparatus.
With chase combining the retransmission uses the same codeword size and same RV parameters (RV=redundancy version), i.e. puncturing patterns, as the first transmission. By applying common incremental redundancy, the retransmission uses a different puncturing pattern than in the first transmission. When using an advanced incremental redundancy, only a subset of the information bits or none of the information bits of the first transmission and only different parity bits than of the first transmission are sent by the retransmission for consuming less radio link capacity.
So-called segmented HARQ is a HARQ technique, where a data packet P is partitioned into N segments. For each segment a receiver of the segment reports an ACK/NACK message to the transmitter to indicate whether the segment was correctly received. Segments for which the transmitter receives a NACK will be retransmitted, e.g. by applying incremental redundancy or chase combining.
A HARQ scheme using network coding applies a joint retransmission of two or more data segments. Therefore, a data segment for the joint retransmission is obtained for example by superimposing so-called hard bits of the two or more data segments for example by modulo 2 addition.